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### Question: What causes Hyperemesis gravidarum?
### Response: Nearly all women have some nausea or vomiting, or morning sickness, particularly during the first 3 months of pregnancy.
The cause of nausea and vomiting during pregnancy is believed to be rapidly rising blood levels of a hormone called HCG (human chorionic gonadotropin), which is released by the placenta.
Extreme nausea and vomiting during pregnancy can happen if you are pregnant with twins (or more) or if you have a hydatidiform mole.